(1) FORCES ACTING ON IONS

• Concentration or chemical gradient:

  • Cl ions are present in higher concentration in the extracellular fluid than in the cell interior, leading to diffusion into the cell
• Electrical gradient:

  • The interior of the cell is negative compared to the exterior, causing Cl- ions to be pushed out of the cell
• An equilibrium is reached over time, where Cl influx equals Cl efflux
• Potassium (K+):

  • Concentration gradient is outward, while the electrical gradient is inward
• Sodium (Na+):

  • Chemical gradient is inward, and the electrical gradient is also inward
• Chloride (Cl-):

  • Concentration gradient is inward, while the electrical gradient is outward
• For K+ and Na+ ions:

  • Intracellular concentration remains constant due to active transport of Na+ out of the cell against its electrical and concentration gradients
  • Active transport of K+ into the cell also contributes to this balance
• The active transport mechanism known as the Sodium-Potassium Pump:

  • Responsible for moving Na+ out of the cell and K+ into the cell
  • Extrudes 3 Na+ from the cell for every 2 K+ it takes into the cell
• Calcium (Ca++):

  • Intracellular concentration is very low, leading to both electrical and concentration gradients directed inward
• The distribution of ions across the cell membrane and the membrane's properties contribute to the presence of membrane potential